The present invention relates generally to turbine plant construction, and more specifically, to a support arrangement that achieves more uniform thermal growth of the turbine rotor and the turbine shell thereby enabling reduced clearance at the rotor/shell interface.
In some current steam turbine designs, clearance closure at the “pinch point” between the rotor and the turbine shell may be on the order of 0.010 inch during turbine operation due to the difference in vertical growth of the rotor bearing supports (or bearing blocks) and the turbine shell-arm supports during turbine operation. Rotor vertical fall and rise, due to thermal growth and contraction of the bearing block is relatively fast (less than an hour), while shell-arm vertical rise and fall due to thermal growth and contraction of the shell support structure is relatively slow (about 16 hours to achieve full growth). In this regard, assumptions that rotor growth and shell growth at turbine standards are substantially equal because lubricant temperatures drive both growths have been proven to be incorrect.
Every mil of clearance between the turbine rotor structure and the turbine shell causes significant leakage loss, and resulting performance and monetary losses. While there have been attempts to achieve more uniform thermal growth characteristics as between the rotor and the shell to reduce leakage loss, such attempts have fallen short of desired goals.